As one of them is already flying J, your GO status will allow you to guest one person on an OW flight. It seems that you don't need to do anything.
The person flying in J should have his own invitation, and your invitation with a GO status allows one guest.
A superior flying in a lower cabin may not may not be an issue. I live in the US, and this happens often. Years ago, one of my colleagues flied to Japan monthly and was upgraded to F every time. Once a while the CEO traveled with him and was stuck in the business class. It didn't concern the CEO a bit.